Known automatic or automated motor vehicle gearboxes normally feature a parking lock which can mechanically fix an output shaft of the gearbox. In addition to a purely mechanical system for actuating this kind of parking lock by way of a mechanical functional connection between a selector lever operable by the driver in the interior of the motor vehicle and the parking lock in the gearbox, electromechanical and electrohydraulic systems are also known for actuating this type of parking lock—for example from DE 41 27 991 C2—in which the parking lock in the gearbox is connected, via an electric functional connection, with a selector device operable by the driver in the interior of the motor vehicle, and in which the parking lock can be electromechanically or electrohydraulically actuated by way of a parking-brake function implemented in an electronic control device of the gearbox, depending on a drive position selected on the selector device and depending on other operating parameters of the motor vehicle.
In addition, there are various known methods of automatically engaging this kind of parking lock. U.S. Pat. No. 3,937,105 proposes automatically engaging the parking lock of the gearbox independently of the driving position selected by the driver if an ignition circuit of the motor vehicle is interrupted and the motor vehicle is still rolling at a speed that is lower than a defined low threshold value.
A method is known from U.S. Pat. No. 4,892,014 in which the parking lock of the gearbox is automatically engaged by way of an electric motor when an ignition circuit of the motor vehicle is uninterrupted and, at the same time, the vehicle speed is lower than a defined low threshold value, and when the driver door of the motor vehicle is open and, simultaneously, the driver seat of the motor vehicle is unoccupied and the vehicle speed is lower than the cited low threshold value. In both cases, it is provided that when the parking lock is automatically engaged, a parking brake of the motor vehicle is actuated as well. In U.S. Pat. No. 4,892,014, it is also proposed that when the ignition circuit is closed when the drive motor of the motor vehicle is not running, the gearbox automatically switches to its neutral position without a driver request being necessary.
And finally, from EP 0 814 287 B1, a function for automatically engaging the parking lock of an automatic gearbox is known, with which the parking lock in the automatic gearbox is automatically engaged by the gearbox control device when the speed of the motor vehicle is zero and, at the same time, an ignition circuit is interrupted and, while simultaneously, as an additional condition, either a predetermined time interval has passed since the interruption of the ignition circuit, or a vehicle door is opened, but no later—and then as the only condition—than when the ignition key has been removed from the ignition switch. In order to achieve better vehicle availability, it is a special feature in all three cases that the engagement of the parking lock is prevented when the driver, immediately before switching off the motor or within a predetermined time interval after switching off the motor, has selected the neutral drive position with the selector lever.
The object of the present invention is to devise an operator for automatically engaging the parking lock of an automatic or automated gearbox that is an alternative to the state of the art, and which sufficiently protects the vehicle against start-up or rolling that is not intended by the driver and has the least possible impairment of vehicle drivability or movability, while avoiding a change in the operating state of the gearbox or the vehicle that is unexpected by the driver.